Fully automatic help #175
Description
Imagine an autoHelp attribute on the @Command annotation that installs a Help subcommand as well as a mixin with standard usageHelp and versionHelp options.
The help subcommand would show the usage help of the subcommand that follows or (if the help subcommand is the last argument) of the preceding command.
Having a standard mixin with help/version options automatically added is convenient and reduces the annoying IDE warnings that these fields are unused.